The organisation and operation of radio networks is regulated by authorities. In the UK, a region of the ultra high frequency (UHF) band is reserved for broadcasting, in particular for terrestrial television broadcasts. This band is shared between analogue and digital broadcasts.
The UHF band is conveniently divided up into channels. According to one existing system, each channel corresponds to an 8 MHz region of the UHF band at a particular centre frequency. Each channel is represented by a channel number from 21 to 68. For example, in the UK, channel number 21 represents an 8 MHz band having a centre frequency of 474 MHz. Similarly, channel number 22 represents a centre frequency of 482 MHz, channel number 23 represents a centre frequency of 490 MHz, and so on. A different portion of the radio spectrum is divided into channels used for radio (i.e. audio) broadcasts. Channel numbering and frequencies may vary between different countries and authorities.
The operation of radio networks is regulated. Therefore, information indicating which channel numbers are in use may be available. The information may also indicate the relationship between a particular channel number and its corresponding frequency. This information is usually referred to as a “frequency plan” of a country.
When a user turns on receiving device, they may not know which networks and/or television channels, or bundles, are available and at which frequencies, or channel numbers, these television channels are transmitted. Thus, it is usually necessary to perform a signal search.
It is particularly important to perform a signal search quickly and efficiently when a receiving device moves between the coverage of two different transmitters, a so-called “handover”. As the user moves between the coverage of one transmitter to another, they may “lose” a signal and need to find a replacement signal. If a search for replacement signals is performed automatically, a user can experience substantially uninterrupted viewing of a particular television channel following a handover.
It is possible to provide information frequencies, or channel numbers, at which television channels are transmitted in a certain network. This information may be provided in service announcements, such as in an NIT or equivalents thereof.
In a DVB-H network, plural television channels are multiplexed into a single signal. In addition to the plural television channels, the signal may also carry radio programmes and data services. Thus, upon receiving a multiplexed signal, a user can provided with plural television channels and/or radio programmes by simply tuning to a single frequency or channel number.
As an example of the present situation in Finland, a signal can carry one of three bundles: Bundle A, Bundle B and Bundle C. Bundle A contains five digital television channels, TV1-D and TV2-D, FST, YLE24 and YLE Teema, and four radio programmes, YLE Classic, YLE Radio Peili, YLEQ, YLE Radio Vega+, some of which are transmitted simultaneously at FM frequencies. TV1-D and TV2-D are simultaneously transmitted in analogue form.
Table 1 below shows which Finnish television channels and radio programmes are included in Bundles A, B and C.
TABLE 1Bundle ABundle BBundle CTelevisionTV1-D,MTV3,CANAL + Finland (m),channelsTV2-D, FST,MTV3+,CANAL + FILM1 (m),YLE24, YLESubtv,CANAL + FILM2 (m),TeemaNelonen,CANAL + Sport (m),NelonenSports channelPlusRegional——Turku TV (In Turku area),televisionTVT Lahti (in Lahti area)channelsand Kuopion Alue-TV(in Kuopio area)RadioYLE Classic,—KissFM, POPprogrammesYLE RadioPeili, YLEQ,YLE RadioVega+MTV3, Subtv and Nelonen are also transmitted on an analogue network. CANAL channels are also transmitted on a satellite network. Thus, by tuning to a frequency or channel number corresponding to a signal that carries Bundle A, the user may choose between five television channels and four radio programmes.
Most countries requite transmitters at least two locations in order to provide reasonable coverage throughout the country. Transmitters at different locations generally transmit the same television channels at different frequencies, i.e. on different channel numbers, so as to minimise interference. Thus, it is usually necessary to perform a signal search each time a user leaves the coverage area of one transmitter and enters the coverage area of another transmitter. One way in which to do this is to perform a signal search across the entire frequency range.
However, performing a full signal search can be time consuming, especially when many channels are spread over a wide bandwidth. It can also constitute a significant drain of the power resources of a mobile device, thereby potentially reducing the interval between battery recharges.